1. Field of the Invention
This invention is concerned with a dialkylbenzene isomer mixture of ethyltoluene or diethylbenzene containing in excess of about 90 weight percent of the para isomer, less than about 10 weight percent of the meta isomer and substantially devoid of the ortho isomer.
2. DESCRIPTION OF THE PRIOR ART
Various mixtures of dialkylbenzene isomers have heretofore been known. In these known mixtures, the para isomer has generally been present in an amount less than about 40 weight percent. Generally, the meta isomer has been present in major proportion, together with smaller amounts of the ortho isomer. Thus, U.S. Pat. No. 2,763,702 describes a mixture of ethyltoluene isomers resulting from ethylation of toluene with ethylene in the presence of a Friedel-Crafts catalyst, such as aluminum chloride, containing isomeric mono-ethyltoluenes in relative proportions of from 8 to 30 percent of the ortho isomer, 40 to 65 percent of the meta isomer and from 20 to 40 percent of the para isomer. U.S. Pat. No. 2,773,862 also describes ethylation of toluene in the presence of an aluminum chloride catalyst to yield an isomeric mixture in which the meta isomer predominates, the para isomer is present to a lesser degree and the ortho isomer is present in still smaller amount. A typical isomer mixture disclosed is one containing 10 to 20 weight percent of ortho-ethyltoluene, 25 to 30 weight percent of para-ethyltoluene and 55 to 60 weight percent of meta-ethyltoluene. U.S. Pat. No. 2,920,119 refers to a conventional ethyltoluene isomer mixture obtained by ethylation of toluene in the presence of a Friedel-Crafts catalyst as one having a meta isomer content of 72 percent, a para isomer content of 20 percent and an ortho isomer content of 8 percent. In accordance with the process of this patent, the proportion of the para isomer is increased relative to the other isomers possibly by a combination of alkylation, disproportionation and isomerization steps to yield a resulting ethyltoluene isomer mixture which may contain about 20 percent of the ortho isomer, 50 percent of the meta isomer and 30 percent of the para isomer. U.S. Pat. No. 3,720,725 discloses a reaction product mixture containing about 45 percent of ortho-ethyltoluene, about 38 percent para-ethyltoluene and about 3 percent of meta-ethyltoluene. Such reaction mixture is obtained as the result of aromatic hydrocarbon alkylation utilizing a catalyst composition comprising a molybdenum halide, an alkylaluminum dihalide and a proton donor.
While the above noted prior art is considered of interest in connection with the subject matter of the present invention, none of such prior art has disclosed an ethyltoluene or diethylbenzene isomer mixture containing from about 90 to about 99 weight percent of the para isomer, about 1 to about 10 weight percent of the meta isomer and substantially devoid, i.e., containing less than 0.1 weight percent of the ortho isomer.
Ethyltoluene and diethylbenzene are valuable chemicals. Ethyltoluene, for example, may be dehydrogenated to produce the corresponding vinyl toluene. It has heretofore been recognized that the presence of substantial quantities of the ortho isomer is highly undesirable in the charge undergoing dehydrogenation since it tends to lead to ring closure with formation of indenes and indanes which adversely effect the properties of the resultant polymer. The indenes and indanes are difficult to separate from the desired vinyl toluene. It has accordingly heretofore been necessary to remove the ortho isomer from the ethyltoluene charge stocks by expensive distillation techniques prior to dehydrogenation thereof.
It is evident that the availability of ethyltoluene or diethylbenzene in which the ortho isomer is initially absent or present only in trace amount would eliminate the necessity for expensive prior removal of this isomer. Such products have, however, not heretofore been available.